Evaluation of cisplatin-induced injury in human kidney organoids

Urine-derived stem cells display homing, incorporation, and regeneration in human organoid and mouse models of acute kidney injury

Urine-derived stem cells (USCs) are adult human stem cells that can be collected noninvasively from urine and cultured in vitro. Because of their renal origin and reported therapeutic effects, we hypothesized that USCs would home to the injured kidney in acute kidney injury (AKI) models. We used mouse models of glycerol-induced rhabdomyolysis or unilateral nephrectomy with clamping ischemia reperfusion injury to model AKI. To track USC homing by live animal imaging, we administered luciferase-expressing (Luc) USCs to mice by intraperitoneal injection. We observed USC localization to both the tubules and glomeruli of injured mice within 3 h by histology. We confirmed the presence of Luc-USCs in the kidney at 3 h, 24 h, and 48 h after the injection using biodistribution analysis of quantitative bioluminescence tomography imaging. We performed immunostaining for kidney injury molecule-1 (KIM-1/HAVCR1/TIM-1) for kidney injury and found reduced expression in USC-treated group at 24 h after injection. To evaluate the effects of the human USCs on injured human nephrons, we injured human kidney organoids with the nephrotoxin cisplatin (5 μM) followed by 5 × 104 USC treatment. USCs were incorporated and lowered expression of KIM-1 in the organoids. USCs home to injured nephrons and reduce measures of kidney injury.

Lebanese Cannabis sativa L. extract protects from cisplatin-induced nephrotoxicity in mice by inhibiting podocytes apoptosis

BACKGROUND

Cisplatin is an anti-cancer drug used to treat a plethora of solid tumors. However, it is associated with dose dependent nephrotoxicity limiting its use as anticancer agent.

OBJECTIVE

The current study aimed to investigate the nephroprotective effect of native Lebanese Cannabis sativa in both in vitro and in vivo mice model of cisplatin-induced nephrotoxicity.

METHODS

Podocytes cell viability was assessed using MTS assay with cisplatin (30µM) in presence or absence of Cannabis oil extract (COE) at 0.5, 1 and 2µg/ml for 24h. Acute renal injury was established in adult female C57BL/6 mice with 20mg/kg, i.p. single dose cisplatin. Mice were divided into control group (vehicle), COE group, cisplatin group and cisplatin plus COE (2.5, 5 and 20mg/kg, i.p.). Animal body weight, serum creatinine, blood urea nitrogen (BUN), and proteinuria were measured.

RESULTS

Cell viability assay and western blot analysis revealed that COE prevented apoptosis induced by cisplatin in cultured immortalized rat podocytes. In addition, in vitro scratch assay demonstrated the ability of COE to promote and restore the migratory capacity of podocytes in cisplatin-treated cells. Interestingly, COE treatment improved urinary and serum parameters characterized by a significant decrease in serum creatinine, urea, and proteinuria at various COE doses. Western blot analysis showed that COE inhibited COX-2 protein induction as well as apoptosis marker production (Bax/Bcl2 ratio) in cisplatin-treated mice when compared to mice treated with cisplatin alone.

CONCLUSION

Collectively, the aforementioned findings indicate that COE could be a promising approach to protect against cisplatin-induced nephrotoxicity.

Improved bioavailability of polydatin and its protective effect against cisplatin induced nephrotoxicity through self-assembled fucoidan and carboxymethyl chitosan delivery system

Cisplatin induced acute kidney injury (AKI) is clinically prevalent, with a complex pathogenesis and a lack of effective therapeutic drugs. Polydatin (Po) has excellent biological activity, but its low solubility and bioavailability limit its application. In this study, fucoidan (Fu) and carboxymethyl chitosan (Cs) self-assembled into nanoparticles through electrostatic interactions/hydrogen bonding and loaded Po (Fu/Cs Po NPs). In vitro studies found that Fu/Cs Po NPs protected human renal tubular epithelial (HK-2) cells from cisplatin induced damage and accumulation of reactive oxygen species (ROS). Mechanistic studies showed that Fu/Cs Po NPs inhibited cisplatin induced DNA damage and activation of cyclic guanosine monophosphate synthase (cGAS) and intron gene stimulator (STING) pathways. In vivo studies showed that Fu/Cs Po NPs treatment alleviated cisplatin induced AKI symptoms, including elevated blood urea nitrogen (BUN) and serum creatinine (SCr), as well as pathological damage to kidney tissues. In vivo mechanism studies also showed that Fu/Cs Po NPs treatment inhibited cisplatin induced DNA damage and activation of the cGAS-STING pathway. The pharmacokinetic and tissue distribution results demonstrated that the Fu/Cs delivery system enhanced the bioavailability and kidney accumulation of Po in vivo. In summary, our study provided potential drugs for the treatment of cisplatin induced AKI.

Slc25a21 in cisplatin-induced acute kidney injury: a new target for renal tubular epithelial protection by regulating mitochondrial metabolic homeostasis

Acute kidney injury (AKI) is a significant global health issue, which is often caused by cisplatin therapy and characterized by mitochondrial dysfunction. Restoring mitochondrial homeostasis in tubular cells could exert therapeutic effects. Here, we investigated Slc25a21, a mitochondrial carrier, as a potential target for AKI intervention. Renal Slc25a21 expression is negatively associated with kidney function in both AKI patients and cisplatin-induced murine models. Sustaining renal expression of Slc25a21 slowed down AKI progression by reducing cellular apoptosis, necroptosis, and the inflammatory response, likely through its regulation of 2-oxoadipate conversion. Slc25a21 is highly expressed in proximal tubular epithelial cells, and its down-regulation contributes to compromised mitochondrial biogenesis and integrity, as well as impaired oxidative phosphorylation. Mechanistically, reduced Slc25a21 in AKI disrupts mitochondrial 2-oxoadipate transport, affecting related metabolites influx and the tricarboxylic acid cycle. These findings demonstrate a previously unappreciated metabolic function of Slc25a21 in tubular cells, and suggest that targeting mitochondrial metabolic homeostasis by sustaining Slc25a21 expression could be a potential novel therapeutic strategy for AKI.

Proximal tubule cell maturation rate and function are controlled by PPARα signaling in kidney organoids

Human pluripotent stem cell-derived kidney organoids are expected to be a useful tool for new drug discoveries, however, the immaturation of kidney organoids causes difficulties in recapitulating renal pharmacokinetics using organoids. Here, we performed time-course single-cell RNA sequencing of kidney organoids and revealed cell heterogeneity in the maturation rate of the proximal tubule. An unbiased analysis to identify upstream targets of genes that are expressed differentially between cells with low and high maturation rates revealed a higher activation of PPARα signaling in rapidly maturing cells. Treatment with a combination of a PPARα agonist and an RXRα agonist induced genes related to proximal tubule maturation and increased the capacity for protein uptake as well as the sensitivity to nephrotoxicity by cisplatin. This method to promote the maturation rate of proximal tubule cells has the potential to be utilized in microphysiological systems to recapitulate proximal tubule functions and to screen nephrotoxic drugs.

Scalable production of uniform and mature organoids in a 3D geometrically-engineered permeable membrane

The application of organoids has been limited by the lack of methods for producing uniformly mature organoids at scale. This study introduces an organoid culture platform, called UniMat, which addresses the challenges of uniformity and maturity simultaneously. UniMat is designed to not only ensure consistent organoid growth but also facilitate an unrestricted supply of soluble factors by a 3D geometrically-engineered, permeable membrane-based platform. Using UniMat, we demonstrate the scalable generation of kidney organoids with enhanced uniformity in both structure and function compared to conventional methods. Notably, kidney organoids within UniMat show improved maturation, showing increased expression of nephron transcripts, more in vivo-like cell-type balance, enhanced vascularization, and better long-term stability. Moreover, UniMat's design offers a more standardized organoid model for disease modeling and drug testing, as demonstrated by polycystic-kidney disease and acute kidney injury modeling. In essence, UniMat presents a valuable platform for organoid technology, with potential applications in organ development, disease modeling, and drug screening.

Co-targeting CDK 4/6 and C-MYC/STAT3/CCND1 axis and inhibition of tumorigenesis and epithelial-mesenchymal-transition in triple negative breast cancer by Pt(II) complexes bearing NH3 as trans-co-ligand

In search of potential anticancer agents, we synthesized SNO-donor salicylaldimine main ligand-based Pt(II) complexes bearing NH3 as co-ligand at trans-position (C1-C6). These complexes showed similarity in structure with transplatin as the two N donor atoms of the main ligand and NH3 co-ligand were coordinated to Pt in trans position to each other. Each complex with different substituents on the main ligand was characterized thoroughly by detailed spectroscopic and spectrophotometric methods. Four of these complexes were studied in solid state by single crystal X-ray analysis. The stability of reference complex C1 was measured in solution state in DMSO‑d6 or its mixture with D2O using 1H NMR methods. These complexes were further investigated for their anticancer activity in triple-negative-breast (TNBC) cells including MDA-MB-231, MDA-MB-468 and MDA-MB-436 cells. All these complexes showed satisfactory cytotoxic effect as revealed by the MTT results. Importantly, the highly active complex C4 anticancer effect was compared to the standard chemotherapeutic agents including cisplatin, oxaliplatin and 5-fluorouracil (5-FU). Functionally, C4 suppressed invasion, spheroids formation ability and clonogenic potential of cancer cells. C4 showed synergistic anticancer effect when used in combination with palbociclib, JQ1 and paclitaxel in TNBC cells. Mechanistically, C4 inhibited cyclin-dependent kinase (CDK)4/6 pathway and targeted the expressions of MYC/STAT3/CCND1/CNNE1 axis. Furthermore, C4 suppressed the EMT signaling pathway that suggested a role of C4 in the inhibition of TNBC metastasis. Our findings may pave further in detailed mechanistic study on these complexes as potential chemotherapeutic agents in different types of human cancers.

Identification of TACSTD2 as novel therapeutic targets for cisplatin-induced acute kidney injury by multi-omics data integration

Cisplatin-induced acute kidney injury (CP-AKI) is a common complication in cancer patients. Although ferroptosis is believed to contribute to the progression of CP-AKI, its mechanisms remain incompletely understood. In this study, after initially processed individual omics datasets, we integrated multi-omics data to construct a ferroptosis network in the kidney, resulting in the identification of the key driver TACSTD2. In vitro and in vivo results showed that TACSTD2 was notably upregulated in cisplatin-treated kidneys and BUMPT cells. Overexpression of TACSTD2 accelerated ferroptosis, while its gene disruption decelerated ferroptosis, likely mediated by its potential downstream targets HMGB1, IRF6, and LCN2. Drug prediction and molecular docking were further used to propose that drugs targeting TACSTD2 may have therapeutic potential in CP-AKI, such as parthenolide, progesterone, premarin, estradiol and rosiglitazone. Our findings suggest a significant association between ferroptosis and the development of CP-AKI, with TACSTD2 playing a crucial role in modulating ferroptosis, which provides novel perspectives on the pathogenesis and treatment of CP-AKI.

Allenamides as a Powerful Tool to Incorporate Diversity: Thia-Michael Lipidation of Semisynthetic Peptides and Access to β-Keto Amides

Lipopeptides are an important class of biomolecules for drug development. Compared with conventional acylation, a chemoselective lipidation strategy offers a more efficient strategy for late-stage structural derivatisation of a peptide scaffold. It provides access to chemically diverse compounds possessing intriguing and non-native moieties. Utilising an allenamide, we report the first semisynthesis of antimicrobial lipopeptides leveraging a highly efficient thia-Michael addition of chemically diverse lipophilic thiols. Using chemoenzymatically prepared polymyxin B nonapeptide (PMBN) as a model scaffold, an optimised allenamide-mediated thia-Michael addition effected rapid and near quantitative lipidation, affording vinyl sulfide-linked lipopeptide derivatives. Harnessing the utility of this new methodology, 22 lipophilic thiols of unprecedented chemical diversity were introduced to the PMBN framework. These included alkyl thiols, substituted aromatic thiols, heterocyclic thiols and those bearing additional functional groups (e.g., amines), ultimately yielding analogues with potent Gram-negative antimicrobial activity and substantially attenuated nephrotoxicity. Furthermore, we report facile routes to transform the allenamide into a β-keto amide on unprotected peptides, offering a powerful "jack-of-all-trades" synthetic intermediate to enable further peptide modification.

Progress and breakthroughs in human kidney organoid research

The three-dimensional (3D) kidney organoid is a breakthrough model for recapitulating renal morphology and function in vitro, which is grown from stem cells and resembles mammalian kidney organogenesis. Currently, protocols for cultivating this model from induced pluripotent stem cells (iPSCs) and patient-derived adult stem cells (ASCs) have been widely reported. In recent years, scientists have focused on combining cutting-edge bioengineering and bioinformatics technologies to improve the developmental accuracy of kidney organoids and achieve high-throughput experimentation. As a remarkable tool for mechanistic research of the renal system, kidney organoid has both potential and challenges. In this review, we have described the evolution of kidney organoid establishment methods and highlighted the latest progress leading to a more sophisticated kidney transformation research model. Finally, we have summarized the main applications of renal organoids in exploring kidney disease.

Applications of 3D organoids in toxicological studies: a comprehensive analysis based on bibliometrics and advances in toxicological mechanisms

A mechanism exploration is an important part of toxicological studies. However, traditional cell and animal models can no longer meet the current needs for in-depth studies of toxicological mechanisms. The three-dimensional (3D) organoid derived from human embryonic stem cells (hESC) or induced pluripotent stem cells (hiPSC) is an ideal experimental model for the study of toxicological effects and mechanisms, which further recapitulates the human tissue microenvironment and provides a reliable method for studying complex cell-cell interactions. This article provides a comprehensive overview of the state of the 3D organoid technology in toxicological studies, including a bibliometric analysis of the existing literature and an exploration of the latest advances in toxicological mechanisms. The use of 3D organoids in toxicology research is growing rapidly, with applications in disease modeling, organ-on-chips, and drug toxicity screening being emphasized, but academic communications among countries/regions, institutions, and research scholars need to be further strengthened. Attempts to study the toxicological mechanisms of exogenous chemicals such as heavy metals, nanoparticles, drugs and organic pollutants are also increasing. It can be expected that 3D organoids can be better applied to the safety evaluation of exogenous chemicals by establishing a standardized methodology.

Stepwise developmental mimicry generates proximal-biased kidney organoids

The kidney maintains body fluid homeostasis by reabsorbing essential compounds and excreting waste. Proximal tubule cells, crucial for renal reabsorption of a range of sugars, ions, and amino acids, are highly susceptible to damage, leading to pathologies necessitating dialysis and kidney transplants. While human pluripotent stem cell-derived kidney organoids are used for modeling renal development, disease, and injury, the formation of proximal nephron cells in these 3D structures is incomplete. Here, we describe how to drive the development of proximal tubule precursors in kidney organoids by following a blueprint of in vivo human nephrogenesis. Transient manipulation of the PI3K signaling pathway activates Notch signaling in the early nephron and drives nephrons toward a proximal precursor state. These "proximal-biased" (PB) organoid nephrons proceed to generate proximal nephron precursor cells. Single-cell transcriptional analyses across the organoid nephron differentiation, comparing control and PB types, confirm the requirement of transient Notch signaling for proximal development. Indicative of functional maturity, PB organoids demonstrate dextran and albumin uptake, akin to in vivo proximal tubules. Moreover, PB organoids are highly sensitive to nephrotoxic agents, display an injury response, and drive expression of HAVCR1 / KIM1 , an early proximal-specific marker of kidney injury. Injured PB organoids show evidence of collapsed tubules, DNA damage, and upregulate the injury-response marker SOX9 . The PB organoid model therefore has functional relevance and potential for modeling mechanisms underpinning nephron injury. These advances improve the use of iPSC-derived kidney organoids as tools to understand developmental nephrology, model disease, test novel therapeutics, and for understanding human renal physiology.

Kidney Disease Modeling with Organoids and Organs-on-Chips

Kidney disease is a global health crisis affecting more than 850 million people worldwide. In the United States, annual Medicare expenditures for kidney disease and organ failure exceed $81 billion. Efforts to develop targeted therapeutics are limited by a poor understanding of the molecular mechanisms underlying human kidney disease onset and progression. Additionally, 90% of drug candidates fail in human clinical trials, often due to toxicity and efficacy not accurately predicted in animal models. The advent of ex vivo kidney models, such as those engineered from induced pluripotent stem (iPS) cells and organ-on-a-chip (organ-chip) systems, has garnered considerable interest owing to their ability to more accurately model tissue development and patient-specific responses and drug toxicity. This review describes recent advances in developing kidney organoids and organ-chips by harnessing iPS cell biology to model human-specific kidney functions and disease states. We also discuss challenges that must be overcome to realize the potential of organoids and organ-chips as dynamic and functional conduits of the human kidney. Achieving these technological advances could revolutionize personalized medicine applications and therapeutic discovery for kidney disease.

Interferon-γ induces combined pyroptotic angiopathy and APOL1 expression in human kidney disease

Elevated interferon (IFN) signaling is associated with kidney diseases including COVID-19, HIV, and apolipoprotein-L1 (APOL1) nephropathy, but whether IFNs directly contribute to nephrotoxicity remains unclear. Using human kidney organoids, primary endothelial cells, and patient samples, we demonstrate that IFN-γ induces pyroptotic angiopathy in combination with APOL1 expression. Single-cell RNA sequencing, immunoblotting, and quantitative fluorescence-based assays reveal that IFN-γ-mediated expression of APOL1 is accompanied by pyroptotic endothelial network degradation in organoids. Pharmacological blockade of IFN-γ signaling inhibits APOL1 expression, prevents upregulation of pyroptosis-associated genes, and rescues vascular networks. Multiomic analyses in patients with COVID-19, proteinuric kidney disease, and collapsing glomerulopathy similarly demonstrate increased IFN signaling and pyroptosis-associated gene expression correlating with accelerated renal disease progression. Our results reveal that IFN-γ signaling simultaneously induces endothelial injury and primes renal cells for pyroptosis, suggesting a combinatorial mechanism for APOL1-mediated collapsing glomerulopathy, which can be targeted therapeutically.

Advancing preclinical drug evaluation through automated 3D imaging for high-throughput screening with kidney organoids

High-throughput drug screening is crucial for advancing healthcare through drug discovery. However, a significant limitation arises from availablein vitromodels using conventional 2D cell culture, which lack the proper phenotypes and architectures observed in three-dimensional (3D) tissues. Recent advancements in stem cell biology have facilitated the generation of organoids-3D tissue constructs that mimic human organsin vitro. Kidney organoids, derived from human pluripotent stem cells, represent a significant breakthrough in disease representation. They encompass major kidney cell types organized within distinct nephron segments, surrounded by stroma and endothelial cells. This tissue allows for the assessment of structural alterations such as nephron loss, a characteristic of chronic kidney disease. Despite these advantages, the complexity of 3D structures has hindered the use of organoids for large-scale drug screening, and the drug screening pipelines utilizing these complexin vitromodels remain to be established for high-throughput screening. In this study, we address the technical limitations of kidney organoids through fully automated 3D imaging, aided by a machine-learning approach for automatic profiling of nephron segment-specific epithelial morphometry. Kidney organoids were exposed to the nephrotoxic agent cisplatin to model severe acute kidney injury. An U.S. Food and Drug Administration (FDA)-approved drug library was tested for therapeutic and nephrotoxicity screening. The fully automated pipeline of 3D image acquisition and analysis identified nephrotoxic or therapeutic drugs during cisplatin chemotherapy. The nephrotoxic potential of these drugs aligned with previousin vivoand human reports. Additionally, Imatinib, a tyrosine kinase inhibitor used in hematological malignancies, was identified as a potential preventive therapy for cisplatin-induced kidney injury. Our proof-of-concept report demonstrates that the automated screening process, using 3D morphometric assays with kidney organoids, enables high-throughput screening for nephrotoxicity and therapeutic assessment in 3D tissue constructs.

A comprehensive review on 3D tissue models: Biofabrication technologies and preclinical applications

The limitations of traditional two-dimensional (2D) cultures and animal testing, when it comes to precisely foreseeing the toxicity and clinical effectiveness of potential drug candidates, have resulted in a notable increase in the rate of failure during the process of drug discovery and development. Three-dimensional (3D) in-vitro models have arisen as substitute platforms with the capacity to accurately depict in-vivo conditions and increasing the predictivity of clinical effects and toxicity of drug candidates. It has been found that 3D models can accurately represent complex tissue structure of human body and can be used for a wide range of disease modeling purposes. Recently, substantial progress in biomedicine, materials and engineering have been made to fabricate various 3D in-vitro models, which have been exhibited better disease progression predictivity and drug effects than convention models, suggesting a promising direction in pharmaceutics. This comprehensive review highlights the recent developments in 3D in-vitro tissue models for preclinical applications including drug screening and disease modeling targeting multiple organs and tissues, like liver, bone, gastrointestinal tract, kidney, heart, brain, and cartilage. We discuss current strategies for fabricating 3D models for specific organs with their strengths and pitfalls. We expand future considerations for establishing a physiologically-relevant microenvironment for growing 3D models and also provide readers with a perspective on intellectual property, industry, and regulatory landscape.

Precision nephrotoxicity testing using 3D in vitro models

Nephrotoxicity is a significant concern during the development of new drugs or when assessing the safety of chemicals in consumer products. Traditional methods for testing nephrotoxicity involve animal models or 2D in vitro cell cultures, the latter of which lack the complexity and functionality of the human kidney. 3D in vitro models are created by culturing human primary kidney cells derived from urine in a 3D microenvironment that mimics the fluid shear stresses of the kidney. Thus, 3D in vitro models provide more accurate and reliable predictions of human nephrotoxicity compared to existing 2D models. In this review, we focus on precision nephrotoxicity testing using 3D in vitro models with human autologous urine-derived kidney cells as a promising approach for evaluating drug safety.

Ascorbate protects human kidney organoids from damage induced by cell-free hemoglobin

Sepsis-associated acute kidney injury is associated with high morbidity and mortality in critically ill patients. Cell-free hemoglobin (CFH) is released into the circulation of patients with severe sepsis and the levels of CFH are independently associated with mortality. CFH treatment increased cytotoxicity in the human tubular epithelial cell line HK-2. To better model the intact kidney, we cultured human kidney organoids derived from induced pluripotent stem cells. We treated human kidney organoids grown using both three-dimensional and transwell protocols with CFH for 48 h. We found evidence for increased tubular toxicity, oxidative stress, mitochondrial fragmentation, endothelial cell injury and injury-associated transcripts compared to those of the untreated control group. To evaluate the protective effect of clinically available small molecules, we co-treated CFH-injured organoids with ascorbate (vitamin C) or acetaminophen for 48 h. We found significantly decreased toxicity, preservation of endothelial cells and reduced mitochondrial fragmentation in the group receiving ascorbate following CFH treatment. This study provides direct evidence that ascorbate or ascorbic acid protects human kidney cells from CFH-induced damage such as that in sepsis-associated acute kidney injury.

14-3-3ζ targets β-catenin nuclear translocation to maintain mitochondrial homeostasis and promote the balance between proliferation and apoptosis in cisplatin-induced acute kidney injury

Cisplatin is a chemotherapeutic agent that is used extensively to treat solid tumors; however, its clinical application is limited by side effects, especially nephrotoxicity. Cisplatin-induced acute kidney injury (AKI) is characterized by DNA damage, cell-cycle arrest, and mitochondrial oxidative stress. Recent research demonstrated that 14-3-3ζ plays an important role in cancers, nerve disease, and kidney disease, although the regulatory mechanisms underlying cisplatin-induced AKI have yet to be fully elucidated. In the present study, we found that 14-3-3ζ mRNA was upregulated in human kidney organoids (GSE145085) when treated with cisplatin; subsequently, this was confirmed in experimental mice. The application of a protein interaction inhibitor for 14-3-3 (BV02) resulted in a decline in renal function, along with apoptosis, mitochondrial dysfunction, and oxidative stress in cisplatin-induced AKI. Accordingly, the knockdown of 14-3-3ζ in cisplatin-treated NRK-52E cells led to increased apoptosis, cell-cycle arrest, the production of reactive oxygen species (ROS), and lipid dysbolism. Furthermore, the blockade of 14-3-3ζ, both in vivo and in vitro, suppressed β-catenin and its nuclear translocation, thus downregulating expression of the downstream gene cyclin D1 in cisplatin-induced damage. In contrast, the overexpression of 14-3-3ζ alleviated the injury caused by cisplatin both in vivo and in vitro. Furthermore, a non-specific agonist of β-catenin, BIO, reversed the effects of 14-3-3ζ knockdown in terms of cisplatin-induced damage in NRK-52E cells by activating β-catenin. Next, we verified the direct interaction between 14 - 3-3ζ and β-catenin by CO-IP and immunofluorescence. Collectively, these findings indicate that 14-3-3ζ protects against cisplatin-induced AKI by improving mitochondrial function and the balance between proliferation and apoptosis by facilitating the nuclear translocation of β-catenin.

Animal Models of Kidney Disease: Challenges and Perspectives

Kidney disease is highly prevalent and affects approximately 850 million people worldwide. It is also associated with high morbidity and mortality, and current therapies are incurable and often ineffective. Animal models are indispensable for understanding the pathophysiology of various kidney diseases and for preclinically testing novel remedies. In the last two decades, rodents continue to be the most used models for imitating human kidney diseases, largely because of the increasing availability of many unique genetically modified mice. Despite many limitations and pitfalls, animal models play an essential and irreplaceable role in gaining novel insights into the mechanisms, pathologies, and therapeutic targets of kidney disease. In this review, we highlight commonly used animal models of kidney diseases by focusing on experimental AKI, CKD, and diabetic kidney disease. We briefly summarize the pathological characteristics, advantages, and drawbacks of some widely used models. Emerging animal models such as mini pig, salamander, zebrafish, and drosophila, as well as human-derived kidney organoids and kidney-on-a-chip are also discussed. Undoubtedly, careful selection and utilization of appropriate animal models is of vital importance in deciphering the mechanisms underlying nephropathies and evaluating the efficacy of new treatment options. Such studies will provide a solid foundation for future diagnosis, prevention, and treatment of human kidney diseases.

Insights into Repeated Renal Injury Using RNA-Seq with Two New RPTEC Cell Lines

Renal proximal tubule epithelial cells (RPTECs) are a primary site for kidney injury. We created two RPTEC lines from CD-1 mice immortalized with hTERT (human telomerase reverse transcriptase) or SV40 LgT antigen (Simian Virus 40 Large T antigen). Our hypothesis was that low-level, repeated exposure to subcytotoxic levels of 0.25-2.5 μM cisplatin (CisPt) or 12.5-100 μM aflatoxin B1 (AFB1) would activate distinctive genes and pathways in these two differently immortalized cell lines. RNA-seq showed only LgT cells responded to AFB1 with 1139 differentially expressed genes (DEGs) at 72 h. The data suggested that AFB1 had direct nephrotoxic properties on the LgT cells. However, both the cell lines responded to 2.5 μM CisPt from 3 to 96 h expressing 2000-5000 total DEGs. For CisPt, the findings indicated a coordinated transcriptional program of injury signals and repair from the expression of immune receptors with cytokine and chemokine secretion for leukocyte recruitment; robust expression of synaptic and substrate adhesion molecules (SAMs) facilitating the expression of neural and hormonal receptors, ion channels/transporters, and trophic factors; and the expression of nephrogenesis transcription factors. Pathway analysis supported the concept of a renal repair transcriptome. In summary, these cell lines provide in vitro models for the improved understanding of repeated renal injury and repair mechanisms. High-throughput screening against toxicant libraries should provide a wider perspective of their capabilities in nephrotoxicity.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Advantages and Potential Benefits of Using Organoids in Nanotoxicology

Organoids are microtissues that recapitulate the complex structural organization and functions of tissues and organs. Nanoparticles have several specific properties that must be considered when replacing animal models with in vitro studies, such as the formation of a protein corona, accumulation, ability to overcome tissue barriers, and different severities of toxic effects in different cell types. An increase in the number of articles on toxicology research using organoid models is related to an increase in publications on organoids in general but is not related to toxicology-based publications. We demonstrate how the quantitative assessment of toxic changes in the structure of organoids and the state of their cell collections provide more valuable results for toxicological research and provide examples of research methods. The impact of the tested materials on organoids and their differences are also discussed. In conclusion, we highlight the main challenges, the solution of which will allow researchers to approach the replacement of in vivo research with in vitro research: biobanking and standardization of the structural characterization of organoids, and the development of effective screening imaging techniques for 3D organoid cell organization.

The "3Ds" of Growing Kidney Organoids: Advances in Nephron Development, Disease Modeling, and Drug Screening

A kidney organoid is a three-dimensional (3D) cellular aggregate grown from stem cells in vitro that undergoes self-organization, recapitulating aspects of normal renal development to produce nephron structures that resemble the native kidney organ. These miniature kidney-like structures can also be derived from primary patient cells and thus provide simplified context to observe how mutations in kidney-disease-associated genes affect organogenesis and physiological function. In the past several years, advances in kidney organoid technologies have achieved the formation of renal organoids with enhanced numbers of specialized cell types, less heterogeneity, and more architectural complexity. Microfluidic bioreactor culture devices, single-cell transcriptomics, and bioinformatic analyses have accelerated the development of more sophisticated renal organoids and tailored them to become increasingly amenable to high-throughput experimentation. However, many significant challenges remain in realizing the use of kidney organoids for renal replacement therapies. This review presents an overview of the renal organoid field and selected highlights of recent cutting-edge kidney organoid research with a focus on embryonic development, modeling renal disease, and personalized drug screening.

Liver Organoids, Novel and Promising Modalities for Exploring and Repairing Liver Injury

The past decades have witnessed great advances in organoid technology. Liver is the biggest solid organ, performing multifaceted physiological functions. Nowadays, liver organoids have been applied in many fields including pharmaceutical research, precision medicine and disease models. Compared to traditional 2-dimensional cell line cultures and animal models, liver organoids showed the unique advantages. More importantly, liver organoids can well model the features of the liver and tend to be novel and promising modalities for exploring liver injury, thus finding potential treatment targets and repairing liver injury. In this review, we reviewed the history of the development of liver organoids and summarized the application of liver organoids and recent studies using organoids to explore and further repair the liver injury. These novel modalities could provide new insights about the process of liver injury.

Large-Scale Production of Kidney Organoids from Human Pluripotent Stem Cells

Kidney organoids differentiated from human pluripotent stem cells (hPSC) have advanced the study of kidney diseases by providing an in vitro system that outperforms traditional monolayer cell culture and complements animal models. This chapter describes a simple two-stage protocol that generates kidney organoids in suspension culture in less than 2 weeks. In the first stage, hPSC colonies are differentiated into nephrogenic mesoderm. In the second stage of the protocol, renal cell lineages develop and self-organize into kidney organoids that contain fetal-like nephrons with proximal and distal tubule segmentation. A single assay generates up to 1000 organoids, thereby providing a rapid and cost-efficient method for the bulk production of human kidney tissue. Applications include the study of fetal kidney development, genetic disease modelling, nephrotoxicity screening, and drug development.

Fucoidan-ferulic acid nanoparticles alleviate cisplatin-induced acute kidney injury by inhibiting the cGAS-STING pathway

Fucoidan (FU) is a natural sulfated polysaccharide with certain biological activity and has been shown to be an excellent nano-delivery material. In this study, ferulic acid (FA)-loaded FU nanoparticles (FA/FU NPs) were prepared and their nephroprotective mechanism was investigated. With a particle size of 158.6 ± 4.5 nm, FA/FU NPs increased the antioxidant activity of FA in vitro, possibly related to the increased dispersity of FA. In vitro results demonstrated that FA/FU NPs significantly protected human renal proximal tubule (HK-2) cells from cisplatin-induced damage, possibly by suppressing cisplatin-induced DNA damage and activating the cGAS-STING pathway. Furthermore, in vivo experiments confirmed that FA/FU NPs protected mice from cisplatin-induced acute kidney injury (AKI). Mechanistic studies confirmed that FA/FU NPs exerted nephroprotective effects by reducing MDA activity and increasing GSH and SOD activity. Our results demonstrated the potential of FU for delivering poorly soluble drug FA and protecting against cisplatin-induced AKI.

Synthesis, Antibacterial Activity, and Nephrotoxicity of Polymyxin B Analogues Modified at Leu-7, d-Phe-6, and the N-Terminus Enabled by S-Lipidation

With the post-antibiotic era rapidly approaching, many have turned their attention to developing new treatments, often by structural modification of existing antibiotics. Polymyxins, a family of lipopeptide antibiotics that are used as a last line of defense in the clinic, have recently developed resistance and exhibit significant nephrotoxicity issues. Using thiol-ene chemistry, the facile preparation of six unique S-lipidated building blocks was demonstrated and used to generate lipopeptide mimetics upon incorporation into solid-phase peptide synthesis (SPPS). We then designed and synthesized 38 polymyxin analogues, incorporating these unique building blocks at the N-terminus, or to replace hydrophobic residues at positions 6 and 7 of the native lipopeptides. Several polymyxin analogues bearing one or more S-linked lipids were found to be equipotent to polymyxin, showed minimal kidney nephrotoxicity, and demonstrated activity against several World Health Organisation (WHO) priority pathogens. The S-lipidation strategy has demonstrated potential as a novel approach to prepare innovative new lipopeptide antibiotics.

Plant vs. Kidney: Evaluating Nephrotoxicity of Botanicals with the Latest Toxicological Tools

Botanicals can cause nephrotoxicity via numerous mechanisms, including disrupting renal blood flow, damaging compartments along the nephron, and obstructing urinary flow. While uncommon, there are various reports of botanical-induced nephrotoxicity in the literature, such as from aristolochia (Aristolochia spp.) and rhubarb (Rheum spp.). However, at present, it is a challenge to assess the toxic potential of botanicals because their chemical composition is variable due to factors such as growing conditions and extraction techniques. Therefore, selecting a single representative sample for an in vivo study is difficult. Given the increasing use of botanicals as dietary supplements and herbal medicine, new approach methodologies (NAMs) are needed to evaluate the potential for renal toxicity to ensure public safety. Such approaches include in vitro models that use layers of physiological complexity to emulate the in vivo microenvironment, enhance the functional viability and differentiation of cell cultures, and improve sensitivity to nephrotoxic insults. Furthermore, computational tools such as physiologically based pharmacokinetic (PBPK) modeling can add confidence to these tools by simulating absorption, distribution, metabolism, and excretion. The development and implementation of NAMs for renal toxicity testing will allow specific mechanistic data to be generated, leading to a better understanding of the nephrotoxic potential of botanicals.

Human kidney organoids model of Esculentoside A nephrotoxicity to investigate the role of epithelial-mesenchymal transition via STING signaling

Radix Phytolaccae (RP) has a long medicinal history and is commonly used to treat systemic edema and ascites in Asia. Although RP is known to cause nephrotoxicity, the role of its main constituent, Esculentoside A (EsA), in nephrotoxicity remains undetermined. We used kidney organoids derived from human inducible pluripotent stem cells (iPSCs) to model EsA nephrotoxicity accurately. Kidney organoids were differentiated and treated with EsA at doses of 0, 15, 30, or 60 μM for 48 h. The in vitro model was compared to a mouse model of EsA nephrotoxicity (intraperitoneally injected, 25 mg·kg^-1). The mechanisms were investigated. Cell viability decreased dose-dependently after treatment with EsA. As polarity was lost, tubular cells decreased, similar to mouse EsA nephrotoxicity with upregulated vimentin expression and a stimulator of the interferon gene (STING). Furthermore, 60 μM EsA could induce endothelial inflammation, lead to mitochondrial damage and activate STING by translocating mtDNA into the cytoplasm to develop an inflammatory cascade and destroy renal endothelial cells with interstitial changes. The data suggest that kidney organoids derived from iPSCs are promising for investigating nephrotoxicity. EsA nephrotoxicity involves the epithelial-mesenchymal transition via STING signaling.

hucMSC-derived exosomes protect ovarian reserve and restore ovarian function in cisplatin treated mice

Anti-cancer therapy often causes premature ovarian insufficiency and infertility as the ovarian follicle reserve is extremely sensitive to chemotherapy drugs, such as cisplatin. Various fertility preservation methods have been explored for women, especially prepubertal girls undergoing radiotherapy and chemotherapy due to cancer. In recent years, mesenchymal stem cell-derived exosomes (MSC-exos) have been reported to play an important role in tissue repair and the treatment of various diseases. In the current study, we observed that human umbilical cord-derived MSC-exos (hucMSC-exos) after short-term culture improved follicular survival and development while receiving cisplatin treatment. Moreover, intravenous injection of hucMSC-exos improved ovarian function and ameliorated inflammatory environment within the ovary. The underlying mechanism of hucMSC-exos on fertility preservation was associated with the down-regulation of p53-related apoptosis and their anti-inflammatory function. Based on these findings, we propose that hucMSC-exos may be a potential approach to improve fertility in women diagnosed with cancer.

What can we learn from kidney organoids?

The ability to generate 3-dimensional models of the developing human kidney via the directed differentiation of pluripotent stem cells-termed kidney organoids-has been hailed as a major advance in experimental nephrology. Although these provide an opportunity to interrogate human development, model-specific kidney diseases facilitate drug screening and even deliver bioengineered tissue; most of these prophetic end points remain to be realized. Indeed, at present we are still finding out what we can learn and what we cannot learn from this approach. In this review, we will summarize the approaches available to generate models of the human kidney from stem cells, the existing successful applications of kidney organoids, their limitations, and remaining challenges.

Functional characterization of ion channels expressed in kidney organoids derived from human induced pluripotent stem cells

Kidney organoids derived from human or rodent pluripotent stem cells have glomerular structures and differentiated/polarized nephron segments. Although there is an increasing understanding of the patterns of expression of transcripts and proteins within kidney organoids, there is a paucity of data regarding functional protein expression, in particular on transporters that mediate the vectorial transport of solutes. Using cells derived from kidney organoids, we examined the functional expression of key ion channels that are expressed in distal nephron segments: the large-conductance Ca2+-activated K+ (BKCa) channel, the renal outer medullary K+ (ROMK, Kir1.1) channel, and the epithelial Na+ channel (ENaC). RNA-sequencing analyses showed that genes encoding the pore-forming subunits of these transporters, and for BKCa channels, key accessory subunits, are expressed in kidney organoids. Expression and localization of selected ion channels was confirmed by immunofluorescence microscopy and immunoblot analysis. Electrophysiological analysis showed that BKCa and ROMK channels are expressed in different cell populations. These two cell populations also expressed other unidentified Ba2+-sensitive K+ channels. BKCa expression was confirmed at a single channel level, based on its high conductance and voltage dependence of activation. We also found a population of cells expressing amiloride-sensitive ENaC currents. In summary, our results show that human kidney organoids functionally produce key distal nephron K+ and Na+ channels.NEW & NOTEWORTHY Our results show that human kidney organoids express key K+ and Na+ channels that are expressed on the apical membranes of cells in the aldosterone-sensitive distal nephron, including the large-conductance Ca2+-activated K+ channel, renal outer medullary K+ channel, and epithelial Na+ channel.

The sugar daddy: the role of the renal proximal tubule in glucose homeostasis

Renal blood flow represents >20% of total cardiac output and with this comes the great responsibility of maintaining homeostasis through the intricate regulation of solute handling. Through the processes of filtration, reabsorption, and secretion, the kidneys ensure that solutes and other small molecules are either returned to circulation, catabolized within renal epithelial cells, or excreted through the process of urination. Although this occurs throughout the renal nephron, one segment is tasked with the bulk of solute reabsorption-the proximal tubule. Among others, the renal proximal tubule is entirely responsible for the reabsorption of glucose, a critical source of energy that fuels the body. In addition, it is the only other site of gluconeogenesis outside of the liver. When these processes go awry, pathophysiological conditions such as diabetes and acidosis result. In this review, we highlight the recent advances made in understanding these processes that occur within the renal proximal tubule. We focus on the physiological mechanisms at play regarding glucose reabsorption and glucose metabolism, emphasize the conditions that occur under diseased states, and explore the emerging class of therapeutics that are responsible for restoring homeostasis.

Live functional assays reveal longitudinal maturation of transepithelial transport in kidney organoids

Kidney organoids derived from hPSCs have opened new opportunities to develop kidney models for preclinical studies and immunocompatible kidney tissues for regeneration. Organoids resemble native nephrons that consist of filtration units and tubules, yet little is known about the functional capacity of these organoid structures. Transcriptomic analyses provide insight into maturation and transporter activities that represent kidney functions. However, functional assays in organoids are necessary to demonstrate the activity of these transport proteins in live tissues. The three-dimensional (3D) architecture adds complexity to real-time assays in kidney organoids. Here, we develop a functional assay using live imaging to assess transepithelial transport of rhodamine 123 (Rh123), a fluorescent substrate of P-glycoprotein (P-gp), in organoids affixed to coverslip culture plates for accurate real-time observation. The identity of organoid structures was probed using Lotus Tetragonolobus Lectin (LTL), which binds to glycoproteins present on the surface of proximal tubules. Within 20 min of the addition of Rh123 to culture media, Rh123 accumulated in the tubular lumen of organoids. Basolateral-to-apical accumulation of the dye/marker was reduced by pharmacologic inhibition of MDR1 or OCT2, and OCT2 inhibition reduced the Rh123 uptake. The magnitude of Rh123 transport was maturation-dependent, consistent with MDR1 expression levels assessed by RNA-seq and immunohistochemistry. Specifically, organoids on day 21 exhibit less accumulation of Rh123 in the lumen unlike later-stage organoids from day 30 of differentiation. Our work establishes a live functional assessment in 3D kidney organoids, enabling the functional phenotyping of organoids in health and disease.

Podocytes derived from human induced pluripotent stem cells: characterization, comparison, and modeling of diabetic kidney disease

BACKGROUND

In diabetic kidney disease, high glucose damages specialized cells called podocytes that filter blood in the glomerulus. In vitro culture of podocytes is crucial for modeling of diabetic nephropathy and genetic podocytopathies and to complement animal studies. Recently, several methods have been published to derive podocytes from human-induced pluripotent stem cells (iPSCs) by directed differentiation. However, these methods have major variations in media composition and have not been compared.

METHODS

We characterized our accelerated protocol by guiding the cells through differentiation with four different medias into MIXL1+ primitive streak cells with Activin A and CHIR for Wnt activation, intermediate mesoderm PAX8+ cells via increasing the CHIR concentration, nephron progenitors with FGF9 and Heparin for stabilization, and finally into differentiated podocytes with Activin A, BMP-7, VEGF, reduced CHIR, and retinoic acid. The podocyte morphology was characterized by scanning and transmission electron microscopy and by flow cytometry analysis for podocyte markers. To confirm cellular identity and niche localization, we performed cell recombination assays combining iPSC-podocytes with dissociated mouse embryonic kidney cells. Finally, to test iPSC-derived podocytes for the modeling of diabetic kidney disease, human podocytes were exposed to high glucose.

RESULTS

Podocyte markers were expressed at similar or higher levels for our accelerated protocol as compared to previously published protocols that require longer periods of tissue culture. We confirmed that the human podocytes derived from induced pluripotent stem cells in twelve days integrated into murine glomerular structures formed following seven days of culture of cellular recombinations. We found that the high glucose-treated human podocytes displayed actin rearrangement, increased cytotoxicity, and decreased viability.

CONCLUSIONS

We found that our accelerated 12-day method for the differentiation of podocytes from human-induced pluripotent stem cells yields podocytes with comparable marker expression to longer podocytes. We also demonstrated that podocytes created with this protocol have typical morphology by electron microscopy. The podocytes have utility for diabetes modeling as evidenced by lower viability and increased cytotoxicity when treated with high glucose. We found that multiple, diverse methods may be utilized to create iPSC-podocytes, but closely mimicking developmental cues shortened the time frame required for differentiation.

High-throughput "read-on-ski" automated imaging and label-free detection system for toxicity screening of compounds using personalised human kidney organoids

Organoid models are used to study kidney physiology, such as the assessment of nephrotoxicity and underlying disease processes. Personalized human pluripotent stem cell-derived kidney organoids are ideal models for compound toxicity studies, but there is a need to accelerate basic and translational research in the field. Here, we developed an automated continuous imaging setup with the "read-on-ski" law of control to maximize temporal resolution with minimum culture plate vibration. High-accuracy performance was achieved: organoid screening and imaging were performed at a spatial resolution of 1.1 μm for the entire multi-well plate under 3 min. We used the in-house developed multi-well spinning device and cisplatin-induced nephrotoxicity model to evaluate the toxicity in kidney organoids using this system. The acquired images were processed via machine learning-based classification and segmentation algorithms, and the toxicity in kidney organoids was determined with 95% accuracy. The results obtained by the automated "read-on-ski" imaging device, combined with label-free and non-invasive algorithms for detection, were verified using conventional biological procedures. Taking advantage of the close-to-in vivo-kidney organoid model, this new development opens the door for further application of scaled-up screening using organoids in basic research and drug discovery.

Kidney organoid research: current status and applications

Organoids are being widely introduced as novel research models in multiple research fields. Human-induced pluripotent stem cells-derived kidney organoids became an indispensable tool to study human kidney development, model various diseases and infections leading to kidney damage, and offer a new route towards better drug development and validation, personalized drug screening, and regenerative medicine. In this review, we provide an update of the most recent developments in kidney organoid induction: their main goals, advantages, and shortcomings. We further discuss their current applications in providing modeling and treatment avenues to various kidney injuries, their use in genome-wide screening of kidney diseases, and the cell interactions occurring in these kidney structures.

Pro-Inflammatory Signalling PRRopels Cisplatin-Induced Toxicity

Cisplatin is a platinum-based chemotherapeutic that has long since been effective against a variety of solid-cancers, substantially improving the five-year survival rates for cancer patients. Its use has also historically been limited by its adverse drug reactions, or cisplatin-induced toxicities (CITs). Of these reactions, cisplatin-induced nephrotoxicity (CIN), cisplatin-induced peripheral neuropathy (CIPN), and cisplatin-induced ototoxicity (CIO) are the three most common of several CITs recognised thus far. While the anti-cancer activity of cisplatin is well understood, the mechanisms driving its toxicities have only begun to be defined. Most of the literature pertains to damage caused by oxidative stress that occurs downstream of cisplatin treatment, but recent evidence suggests that the instigator of CIT development is inflammation. Cisplatin has been shown to induce pro-inflammatory signalling in CIN, CIPN, and CIO, all of which are associated with persisting markers of inflammation, particularly from the innate immune system. This review covered the hallmarks of inflammation common and distinct between different CITs, the role of innate immune components in development of CITs, as well as current treatments targeting pro-inflammatory signalling pathways to conserve the use of cisplatin in chemotherapy and improve long-term health outcomes of cancer patients.

Human Stem Cell and Organoid Models to Advance Acute Kidney Injury Diagnostics and Therapeutics

Acute kidney injury (AKI) is an increasingly common problem afflicting all ages, occurring in over 20% of non-critically ill hospitalized patients and >30% of children and >50% of adults in critical care units. AKI is associated with serious short-term and long-term consequences, and current therapeutic options are unsatisfactory. Large gaps remain in our understanding of human AKI pathobiology, which have hindered the discovery of novel diagnostics and therapeutics. Although animal models of AKI have been extensively studied, these differ significantly from human AKI in terms of molecular and cellular responses. In addition, animal models suffer from interspecies differences, high costs and ethical considerations. Static two-dimensional cell culture models of AKI also have limited utility since they have focused almost exclusively on hypoxic or cytotoxic injury to proximal tubules alone. An optimal AKI model would encompass several of the diverse specific cell types in the kidney that could be targets of injury. Second, it would resemble the human physiological milieu as closely as possible. Third, it would yield sensitive and measurable readouts that are directly applicable to the human condition. In this regard, the past two decades have seen a dramatic shift towards newer personalized human-based models to study human AKI. In this review, we provide recent developments using human stem cells, organoids, and in silico approaches to advance personalized AKI diagnostics and therapeutics.

Inhibition of PLK3 Attenuates Tubular Epithelial Cell Apoptosis after Renal Ischemia–Reperfusion Injury by Blocking the ATM/P53-Mediated DNA Damage Response

Objective

Renal ischemia–reperfusion (I/R) injury is a major cause of acute kidney injury (AKI) in transplanted kidneys. This study was aimed at exploring the role of PLK3 (polo-like kinase 3) in renal I/R injury, focusing on its relationship with oxidative stress-induced DNA damage and renal tubular epithelial cell (TEC) apoptosis.

Methods

TRAP-seq data from the development dataset GSE52004 and the validation dataset GSE121191 were analyzed using GEO2R. PLK3 overexpression plasmids and targeted silencing siRNAs were used in a model of hypoxia/reoxygenation (H/R) injury, and rAAV-9-PLK3-KD were administered to C57BL/6J mice exposed to I/R injury. The ATM-specific inhibitor KU-60019 was used to block the DNA damage response (DDR). Western blotting was performed to measure DDR- and apoptosis-associated protein expression. Cell viability was measured by CCK-8 reagent, and apoptosis was examined by flow cytometry and TUNEL assay. Furthermore, the fluorescent probes H₂DCFH-DA and DHE were used to measure ROS production in vitro. The MDA level and SOD activity were measured to assess oxidative stress in vivo. KIM-1 staining and Scr and BUN were used to evaluate kidney injury.

Results

The mRNA and protein levels of PLK3 were markedly increased in the H/R injury and I/R injury models. GO terms showed that PLK3 was mainly involved in oxidative stress and DNA damage after renal I/R injury. Overexpression of PLK3 decreased cell viability and increased apoptosis. In contrast, targeted silencing of PLK3 expression decreased the Bax/Bcl-2 ratio by decreasing P53 phosphorylation, thereby reducing TEC apoptosis. Furthermore, KU-60019 reduced PLK3 activation and DDR-induced apoptosis, while overexpression of PLK3 reversed the mitigating effect of KU-60019 on TEC apoptosis. Similarly, rAAV-9-PLK3 KD mice exhibited a lower rate of TEC apoptosis and milder renal damage after I/R injury.

Conclusion

We demonstrate for the first time that PLK3 is involved in oxidative stress-induced DNA damage and TEC apoptosis in renal I/R injury. Inhibition of PLK3 attenuates TEC apoptosis after I/R injury by blocking the ATM/P53-mediated DDR. Therefore, PLK3 may serve as a potential therapeutic target for ischemic AKI.

Physiology assays in human kidney organoids

Kidney organoids derived from human pluripotent stem cells constitute a novel model of disease, development, and regenerative therapy. Organoids are human, experimentally accessible, high throughput, and enable reconstitution of tissue-scale biology in a petri dish. Although gene expression patterns in organoid cells have been analyzed extensively, less is known about the functionality of these structures. Here, we review assays of physiological function in human kidney organoids, including best practices for quality control, and future applications. Tubular structures in organoids accumulate specific molecules through active transport, including dextran and organic anions, and swell with fluid in response to cAMP stimulation. When engrafted into animal models in vivo, organoids form vascularized glomerulus-like structures capable of size-selective filtration. Organoids exhibit metabolic, endocrine, injury, and infection phenotypes, although their specificity is not yet fully clear. To properly interpret organoid physiology assays, it is important to incorporate appropriate negative and positive controls, statistical methods, data presentation, molecular mechanisms, and clinical data sets. Improvements in organoid perfusion, patterning, and maturation are needed to enable branching morphogenesis, urine production, and renal replacement. Reconstituting renal physiology with kidney organoids is a new field with potential to provide fresh insights into classical phenomena.

Enhanced metanephric specification to functional proximal tubule enables toxicity screening and infectious disease modelling in kidney organoids

While pluripotent stem cell-derived kidney organoids are now being used to model renal disease, the proximal nephron remains immature with limited evidence for key functional solute channels. This may reflect early mispatterning of the nephrogenic mesenchyme and/or insufficient maturation. Here we show that enhanced specification to metanephric nephron progenitors results in elongated and radially aligned proximalised nephrons with distinct S1 - S3 proximal tubule cell types. Such PT-enhanced organoids possess improved albumin and organic cation uptake, appropriate KIM-1 upregulation in response to cisplatin, and improved expression of SARS-CoV-2 entry factors resulting in increased viral replication. The striking proximo-distal orientation of nephrons resulted from localized WNT antagonism originating from the organoid stromal core. PT-enhanced organoids represent an improved model to study inherited and acquired proximal tubular disease as well as drug and viral responses.

Inwardly rectifying potassium channels mediate polymyxin-induced nephrotoxicity

Polymyxin antibiotics are often used as a last-line defense to treat life-threatening Gram-negative pathogens. However, polymyxin-induced kidney toxicity is a dose-limiting factor of paramount importance and can lead to suboptimal treatment. To elucidate the mechanism and develop effective strategies to overcome polymyxin toxicity, we employed a whole-genome CRISPR screen in human kidney tubular HK-2 cells and identified 86 significant genes that upon knock-out rescued polymyxin-induced toxicity. Specifically, we discovered that knockout of the inwardly rectifying potassium channels Kir4.2 and Kir5.1 (encoded by KCNJ15 and KCNJ16, respectively) rescued polymyxin-induced toxicity in HK-2 cells. Furthermore, we found that polymyxins induced cell depolarization via Kir4.2 and Kir5.1 and a significant cellular uptake of polymyxins was evident. All-atom molecular dynamics simulations revealed that polymyxin B₁ spontaneously bound to Kir4.2, thereby increasing opening of the channel, resulting in a potassium influx, and changes of the membrane potential. Consistent with these findings, small molecule inhibitors (BaCl₂ and VU0134992) of Kir potassium channels reduced polymyxin-induced toxicity in cell culture and mouse explant kidney tissue. Our findings provide critical mechanistic information that will help attenuate polymyxin-induced nephrotoxicity in patients and facilitate the design of novel, safer polymyxins.

Identifying Common Molecular Mechanisms in Experimental and Human Acute Kidney Injury

Acute kidney injury (AKI) is a highly prevalent, heterogeneous syndrome, associated with increased short- and long-term mortality. A multitude of different factors cause AKI including ischemia, sepsis, nephrotoxic drugs, and urinary tract obstruction. Upon injury, the kidney initiates an intrinsic repair program that can result in adaptive repair with regeneration of damaged nephrons and functional recovery of epithelial activity, or maladaptive repair and persistence of damaged epithelial cells with a characteristic proinflammatory, profibrotic molecular signature. Maladaptive repair is linked to disease progression from AKI to chronic kidney disease. Despite extensive efforts, no therapeutic strategies provide consistent benefit to AKI patients. Since kidney biopsies are rarely performed in the acute injury phase in humans, most of our understanding of AKI pathophysiology is derived from preclinical AKI models. This raises the question of how well experimental models of AKI reflect the molecular and cellular mechanisms underlying human AKI? Here, we provide a brief overview of available AKI models, discuss their strengths and limitations, and consider important aspects of the AKI response in mice and humans, with a particular focus on the role of proximal tubule cells in adaptive and maladaptive repair.

Kidney organoids as a promising tool in nephrology

Kidney disease has become a global public health problem affecting over 750 million people worldwide and imposing a heavy economic burden on patients. The complex architecture of the human kidney makes it very difficult to study the pathophysiology of renal diseases in vitro and to develop effective therapeutic options for patients. Even though cell lines and animal models have enriched our understanding, they fail to recapitulate key aspects of human kidney development and renal disease at cellular and functional levels. Organoids can be derived from either pluripotent stem cells or adult stem cells by strictly regulating key signalling pathways. Today, these self-differentiated organoids represent a promising technology to further understand the human kidney, one of the most complex organs, in an unprecedented way. The newly established protocols improved by organ-on-chip and coculture with immune cells will push kidney organoids towards the next generation. Herein, we focus on recent achievements in the application of kidney organoids in disease modelling, nephrotoxic testing, precision medicine, biobanking, and regenerative therapy, followed by discussions of novel strategies to improve their utility for biomedical research. The applications we discuss may help to provide new ideas in clinical fields.

Human Kidney Organoids and Tubuloids as Models of Complex Kidney Disease

Kidney organoids derived from pluripotent stem cells and epithelial organoids derived from adult tissue (tubuloids) have been used to study various kidney disorders with a strong genetic component, such as polycystic kidney disease, Wilms tumor, and congenital nephrotic syndrome. However, complex disorders without clear genetic associations, such as acute kidney injury and many forms of chronic kidney disease, are only just beginning to be investigated using these in vitro approaches. Although organoids are a reductionist model, they contain clinically relevant cell populations that may help to elucidate human-specific pathogenic mechanisms. Thus, organoids may complement animal disease models to accelerate the translation of laboratory proof-of-concept research into clinical practice. This review discusses whether kidney organoids and tubuloids are suitable models for the study of complex human kidney disease and highlights their advantages and limitations compared with monolayer cell culture and animal models.

Advanced human developmental toxicity and teratogenicity assessment using human organoid models

Tremendous progress has been made in the field of toxicology leading to the advance of developmental toxicity assessment. Conventional animal models and in vitro two-dimensional models cannot accurately describe toxic effects and predict actual in vivo responses due to obvious inter-species differences between humans and animals, as well as the lack of a physiologically relevant tissue microenvironment. Human embryonic stem cell (hESC)- and induced pluripotent stem cell (iPSC)-derived three-dimensional organoids are ideal complex and multicellular organotypic models, which are indispensable in recapitulating morphogenesis, cellular interactions, and molecular processes of early human organ development. Recently, human organoids have been used for drug discovery, chemical toxicity and safety in vitro assessment. This review discusses the recent advances in the use of human organoid models, (i.e., brain, retinal, cardiac, liver, kidney, lung, and intestinal organoid models) for developmental toxicity and teratogenicity assessment of distinct tissues/organs following exposure to pharmaceutical compounds, heavy metals, persistent organic pollutants, nanomaterials, and ambient air pollutants. Combining next-generation organoid models with innovative engineering technologies generates novel and powerful tools for developmental toxicity and teratogenicity assessment, and the rapid progress in this field is expected to continue.

Tissue Culture Models of AKI: From Tubule Cells to Human Kidney Organoids

AKI affects approximately 13.3 million people around the world each year, causing CKD and/or mortality. The mammalian kidney cannot generate new nephrons after postnatal renal damage and regenerative therapies for AKI are not available. Human kidney tissue culture systems can complement animal models of AKI and/or address some of their limitations. Donor-derived somatic cells, such as renal tubule epithelial cells or cell lines (RPTEC/hTERT, ciPTEC, HK-2, Nki-2, and CIHP-1), have been used for decades to permit drug toxicity screening and studies into potential AKI mechanisms. However, tubule cell lines do not fully recapitulate tubular epithelial cell properties in situ when grown under classic tissue culture conditions. Improving tissue culture models of AKI would increase our understanding of the mechanisms, leading to new therapeutics. Human pluripotent stem cells (hPSCs) can be differentiated into kidney organoids and various renal cell types. Injury to human kidney organoids results in renal cell-type crosstalk and upregulation of kidney injury biomarkers that are difficult to induce in primary tubule cell cultures. However, current protocols produce kidney organoids that are not mature and contain off-target cell types. Promising bioengineering techniques, such as bioprinting and "kidney-on-a-chip" methods, as applied to kidney nephrotoxicity modeling advantages and limitations are discussed. This review explores the mechanisms and detection of AKI in tissue culture, with an emphasis on bioengineered approaches such as human kidney organoid models.